China is the world's top coke producer. Statistical information shows that China produces 388,000,000 tons of coke in 2010, accounting for 60% of the world's output. The coal-tar resources are abundant in China, wherein the production of the coal-tar recycled from coke-oven gas reaches 18,000,000 tons.
In China, the technical route for processing the high-temperature coal tar is basically an approach of producing BTX Fraction, carbolic oil, naphthalene oil, wash oil, anthracene oil and pitch by distilling the tar, the products of which lack variety. In the recent years, since the project with a coal-tar processing scale of 300,000 tons is implemented, the variety of the refined chemical product therefrom is continually increasing. However, because of the poor yields of these products, it can only be focused on the refining processing of carbolic oil, naphthalene oil, wash oil and anthracene oil for the actual products. Meanwhile, the main problem brought by such processing route is serious environmental pollution. Since the resulted pitch only can be further processed to yield low value-added products such as mid-temperature pitch, modified pitch and pitch coke and so forth, the value of pitch cannot be reflected, which causes the products in the whole project being low added-value, and non-ideal benefits.
There is an increasing and rapidly expanding global need for new materials, especially advanced carbon materials, with the technology progress and the ever-increasing enhancement of environmental protection requirement. All of pitch-based carbon fiber, carbon foam, C/C composite, mesocarbon microbeads and so forth show an extremely wide application prospect. However, the industrial-scale production of novel carbon materials, especially mesophase pitch, a precursor of advanced carbon materials, is bogging down. Most of the technical solutions are still in the experimental stage, rarely to be suitable for the industrial-scale production. The existing industrial production technology of mesophase pitch always face the problems of difficult technologies and high costs, which limit the application and promotion of the novel carbon materials.
The production of needle coke and mesophase pitch from coal tar pitch is always the research hotspot for the Chinese engineers. After years of effort, positive progress has been made in the industrial production of the needle coke. However, because of the inherent limitations of the coal tar pitch, even though extensive research has been carried out, limited success has be accomplished in the field of the mesophase pitch due to either high costs or high industrialization difficulties.
Chinese patent No. CN85107441A introduced a process for producing super needle coke by using a quinine insolubles (QI) free coal tar or coal tar pitch. However, the process has a low degree of catalytic hydrogenation, a difficult technology of direct hydrogenation of coal tar or coal tar pitch, and a short service life of catalyst. This process does not make full use of hydrogenated solvent oil, a byproduct, to optimize itself, which results in losing a great amount of valuable β resin, a low yield of pitch and a low degree of hydrogenation of low boiling point components.
Chinese patent No. CN87103787A introduced a process for producing mesophase pitch for high performance carbon fibers from a coal tar or a petroleum residual oil through thermal treatment and the hydrogenation from solvent. The process requires a lot of xylene, hydrogenated anthracene oil and wash oil solvent which cannot be self-produced by the process, resulting in a high production cost. As a technology for heating processing with multi-stage pyrolysis and flash is employed, it's very easy to cause coking and jamming in system, resulting in difficulties in large-scale continuous production.
Chinese patent No. CN85105609A disclosed a process for hydrogenating coal tar or coal tar pitch, wherein the catalyst metal has a low loading amount and low activity, and was poor in the removal of heteroatom of pitch. The process employed single means of mild catalytic hydrogenation which can hardly change the molecular structure. Moreover, coal tar or coal tar pitch has a high content of colloid and asphaltene, which causes easy carbon deposition and short service life of the catalyst under the fixed bed catalytic conditions and a difficulty in hydrogenation, therefore, an effective hydrogenation in a long run can hardly be achieved.
Chinese patent No. ZL200610032060.7 introduced a process for producing fuel oil by hydrogenation of coal tar, which required converting all distillation fractions of the high-temperature coal tar into naphtha, gasoline and diesel, and had high requirements for the catalyst activity and hydrogenation reaction conditions.
Chinese patent No. CN101074381A introduced a process for processing and utilizing coal tar, the target product of which is gasoline and diesel. It did not mention the research for the pitch therein. The preprocessing of coal tar therein needs to be optimized.
The invention aims at overcoming the disadvantages in the prior art, raising a new approach for processing and utilizing the high-temperature coal tar, and providing a process suitable for industrialization application for producing mesophase pitch from the catalytic hydrogenation of high-temperature coal tar with byproducts such as carbolic oil, crude naphthalene, naphtha and gasoline and diesel blending components, to increase the value of the coal tar processing products by a large margin.